The present invention relates to additives for cements, and more particularly to additives for increasing early strength of cements, methods for improving the early strength of cements, and high early strength cements.
The term xe2x80x9ccementxe2x80x9d has used herein means and refers to hydratable cementitious binder that is used for making materials such as mortar and concrete. Cements may comprise, for example, Ordinary Portland Cement (OPC), or xe2x80x9cblended cements,xe2x80x9d the latter of which can refer to OPC blended with ground limestone or OPC blended with pozzolanic materials to form xe2x80x9cpozzolanicxe2x80x9d cements. Pozzolanic cements therefore typically incorporate one or more of the following pozzolanic materialsxe2x80x94such as slag, metakaolin, fly ash, natural pozzolansxe2x80x94to allow manufacturers to substitute for portions of Portland cement clinker, thereby providing an economic benefit.
There is economic competition between manufacturers of pozzolanic cements and manufacturers of the more expensive ordinary Portland cements (OPC). Customers thus frequently need to choose between OPC and the less expensive pozzolanic cements, which can have comparatively less early strength and a higher water demand. Accordingly, the present inventors believe that novel additives for improving early strength in cements, and in particular pozzolanic cements, while decreasing water demand, are needed.
The present invention provides high early strength cement additives, cement compositions, and methods for increasing early strength in cements and cementitious compositions. The additives of the invention are believed to be useful for pozzolanic cements, blended cements, e.g., Ordinary Portland Cement and ground limestone, as well as OPC by itself, although it is believed that the benefits with pozzolanic cements would be most valued by customers due to reduction of costs.
An exemplary method of the present invention for increasing early strength in cement (e.g., preferably blended cement, and most preferably pozzolanic cement), comprises introducing into the cement, preferably during the grinding thereof, (a) at least one water reducer comprising polyoxyalkylene groups; (b) a sugar; and (c) an alkali or alkaline earth metal chloride. An amine is optionally added into the grinding process in further exemplary methods.
Exemplary additives of the present invention for improving early strength of cement (preferably blended cement, and most preferably pozzolanic cement), comprises (a) at least one water reducer comprising polyoxyalkylene groups; (b) a sugar; (c) an alkali or alkaline earth metal chloride; and (d) optionally an amine. Preferably, the additives are introduced as an aqueous solution during the grinding of the cement. Exemplary cement compositions of the invention comprise a mixture of cement (preferably blended cement, and most preferably pozzolanic cement), in combination with the above-described polyoxyalkylene water reducer, sugar, and alkali or alkaline earth metal chloride.
Further features and advantages of the invention may be described in detail hereinafter.
The present invention can be achieved in the form of an additive (comprising a polyoxyalkylene water reducer, a sugar, and an alkali or alkaline earth metal chloride) which can be added into a cement (preferably blended cement, and most preferably pozzolanic cement) during the grinding stage, or into a cementitious composition (including one that contains blended or pozzolanic cement with fine aggregate (sand) and/or course aggregate (gravel, stones); a cement (or cementitious composition such as masonry cement, mortar, or concrete) containing the aforementioned components (either as an admixture or, more preferably, incorporated during the manufacture of cement as interground additives); and also as a method for improving the early strength of cement by incorporating the additive components during grinding of cement.
Polyoxyalkylene polymers have been used as water reducers for Portland cement. Preferably, the polymers are comb polymers having a backbone and pendant groups, with the polyoxyalkylene groups contained in the backbone, in the pendant groups, or in both. Comb polymer-type water reducers are known and believed to be suitable for use in the present invention. For example, U.S. Pat. 5,393,343 of Darwin et al., which is incorporated fully herein by reference, taught an EO/PO type comb polymer useful as a superplasticizer or water-reducer for retaining in concrete a high degree of slump (e.g., high flowability) over a sustained period of time. The term xe2x80x9cEO/POxe2x80x9d is sometimes synonymous with the term xe2x80x9coxyalkylene groupxe2x80x9d and serves as a convenient short-hand to designate polyoxyalkylene groups which are combinations of ethylene oxide (EO)/propylene oxide (PO) repeating units.
Preferably, an EO/PO type comb polymer is employed having a polymer backbone, e.g., carbon backbone, to which are attached both carboxylate groups (which function as cement anchoring groups in the cementitious mixture) and pendant groups such as ethylene oxide (EO) groups, propylene oxide (PO) groups, and/or a combination of EO/PO groups. The pendant groups may be ionic or non-ionic. Further examples of EO/PO type comb polymer water-reducers are shown in U.S. Pat. Nos. 4,946,904, 4,471,100, 5,100,984 and 5,369,198. These patents describe comb polymers which are, for example, copolymers of, polycarboxylic monomers such as maleic acid or anhydride and polymerizable EO/POxe2x80x94containing monomers such as polyalkylene glycol monoallyl ethers, etc.
In U.S. Pat. No. 5,840,114, there is disclosed an exemplary polyoxyalkylene polymer which may be suitable for the invention. The polymer comprises a carbon containing backbone to which is attached to groups shown by the structures (I) and (II), and optionally groups shown by structures (II) and (IV) as shown below: 
wherein each R independently represents a hydrogen atom or a methyl group (xe2x80x94CH3) group; A represents hydrogen atom, a C1-C10 alkyl group, Rxe2x80x2 or an alkali metal cation or a mixture thereof; Rxe2x80x2 represents a hydrogen atom or a C2-C10 oxyalkylene group represented by (BO)nRxe2x80x3 in which O represents an oxygen atom, B represents a C2-C10 alkylene group, Rxe2x80x3 represents a C1-C10 alkyl and n represents an integer of from 1-200, or mixtures thereof; and a, b, c, and d are numerical values representing molar percentage of the polymer""s structure such that a is a value of about 50-70; the sum of c plus d is at least 2 to a value of (100xe2x88x92a) and is preferably from 3 to 10; and b is not more than [100xe2x88x92(a+c+d)].
(The letter xe2x80x9cBxe2x80x9d is being used for lexographical convenience herein to denote an alkylene group. Those of ordinary skill in the art will realise that xe2x80x9cBxe2x80x9d herein does not represent boron).
A commercially available polyoxyalkylene polymer which is suitable for the purposes of the present invention is available from Grace Construciton Products under the brandname ADVA(copyright). This product is specifically a polyacrylic acid comb polymer made by grafting a polyoxyalkylene amine onto a polycarboxylic acid backbone (amidization/imidization reaction).
Another polyoxyalkylene polymer which is believed to be suitable can be obtained by polymerization of maleic anhydride and an ethylenically-polymerizable polyalkylene, as prepared in U.S. Pat. No. 4,471,100, the entire disclosure of which is incorporated herein by reference. This is believed to be sold in the form of metallic salts formed by final reaction of the polymers with a base such sodium or calcium hydroxide.
It is also contemplated that polyoxyalkylene polymers may not necessarily require comb structures (i.e., backbone with pendant groups), but may have a linear or branched structure, or other structures.
Exemplary polyoxyalkylene polymers will preferably have a molecular weight of between 3,000-100,000 and more preferably 15,000-50,000.
The preferred amount of polyoxyalkylene water reducer used in the invention should be in the range of 0.0002-0.4 percent, and more preferably 0.0025-0.075 percent, based on the dry weight of cement (e.g., Portland cement plus pozzolans).
Exemplary sugars useful in the present invention may be used in dry powder form, but are preferably incorporated in an aqueous solution. Sugars which are conventionally used in the cement and concrete industry may be used in the present invention, and these include glucose, sucrose, fructose, tetrose, pentose, hexose, etc., including corn syrup and molasses. Also useful in the present invention are gluconic acid, heptogluconic acid, and their salts (e.g., gluconate, heptogluconate). A mixture of sodium gluconate and corn syrup, optionally with molasses, is especially preferred. It is believed that other sugars may be used in the invention, such as those derived from or based upon aldonic acid (e.g., gluconic acid, heptogluconic acid), aldaric acid (e.g., glycaric acid, heptoglucaric acid), and uronic acid (e.g., glucuronic acid, heptoglucuronic acid), or their salts or their lactones (i.e. anhydrides).
The sugar or sugars may be used in the present invention, when incorporated into the grinding of cement (preferably blended cement, and most preferably pozzolanic cement), in the amount of 0.0001-0.4 percent, and more preferably 0.0025-0.1 percent, based on the dry weight of the cement
Exemplary alkali or alkaline earth metal chlorides salts useful in the invention include calcium chloride, sodium chloride, potassium chloride, lithium chloride, and ammonium chloride, with calcium chloride being preferred. In solution, these salts will, of course, dissociate into their ionic forms, and thus it will be understood that reference to the salt form, e.g., calcium chloride, will stand also as a description of the ionized calcium and chloride molecules when dissolved into an aqueous solution.
Preferably, the salt is used in the amount of 0.0001-1.0 percent, and more preferably 0.002540.175 percent, based on the dry weight of the cement (e.g., pozzolanic cement).
Optionally, although preferably, exemplary additives and methods of the invention further comprise the use of an amine. Exemplary amines include alanolamines (e.g., triethanolamine, trilsopropanolamine, di(ethanol)isopropanolamine, di(isoproponal)amine, etc.). Preferably, the amine is incorporated into the cement (Portland, blended, or, most preferably, pozzolanic cement) in the amount of 0-0.15 percent, and more preferably 0.0005-0.04 percent, based on the dry weight of the cement. The amines may also be used as acetate salts, formate salts, or acrylate salts. For example, triethanolamine acetates may be employed in the methods, additives, and cement compositions (e.g., blended or pozzolanic cement-based compositions) of the invention, and these may provide improved grinding action and/or reduced pack set of the cement.
Other components may be incorporated into the additives of the invention such as surface active defoaming compounds (e.g., a nonionic surfactant such as BASF PLURONIC(copyright) 25R2 or an alkylphosphate such as tributyl phosphate). The amounts of such defoaming compounds can be upt to 3 or 4% based on the amount of polyoxyalkylene water reducer used.
In preferred methods of the invention, the preferred manner of using the above-described high early strength enhancing additive components is to incorporate them together into an aqueous solution, and then introduce the solution (as one additive) at one time into the grinding of the pozzolanic cement. The use of a solution to introduce this additive is preferred since the components within the additive would be more easily dispensed into the cement grinding process.